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AD7195 Mode and Configuration for Quitest Operation

Question asked by cydrollinger on Dec 4, 2015
Latest reply on Dec 7, 2015 by JellenieR

Current operation of the AD7195 within the system has 16 effective bits converting signal. The system is being investigated for noise source on the analog ground signal due to the digital ground signal, ground loops.  As the investigation of the system continues ground loops are being discontinued and the noise level drops, the ADC7195 becomes the tool to quantify this noise. I am attempting to minimize the noise level on the analog ground by making hardware changes to the analog circuitry and quantifying this by measuring the effective number of bits measured by the ADC7195 with the differential inputs shorted.

First, given that the ADC7195 is setup as shown in the schematic what is the configuration and mode settings that what produce the highest effective number of bits, optimal settings.ADC.png

Current settings are as follows:

Mode   :180400
   MR21 - operating mode see table 23 in DS pg. 21
   MR20 - Enable status register output appended to data read
   MR18 - CLK see DS pg. 20
   MR16 - set to 0
   MR15 - SINC3 filter when set
   MR14 - set to 0
   MR13 - Enable parity
   MR12 - set to 0
   MR11 - single cycle conversion
   MR10 - Enable notch filter at 60Hz
   MR0  - Output data rate = (MCLK/1024)/(MR9-MR0)
    Configuration    :000350-000357
   CR23 - Chop Enable
   CR22 - AC excitation enable when set requires CR23 to be set also
   CR16 - these bit set to 0
   CR15 -
   CR8  - channel select
   CR7  - test current 500nA sourced from ADC onto AIN chop disabled and buffer active
   CR6  - Reference detect function
   CR5  - set to 0
   CR4  - Buffer enable Input source impedance added
   CR3  - Polarity enables between Unipolar or Bipolar
   CR0  - Gain select
   7(111) - 128V/V
   6(110) -  64V/V
   5(101) -  32V/V
   4(100) -  16V/V
   3(011) -   8V/V
   2(010) -   not available
   1(001) -   not available
   0(000) -   1V/V see D.S. pg 24


Lastly, I would like some advice in the best practice of getting the most of the ratiometric method of driving the transducer, a 350 ohm total impedance wheatstone bridge, and measuring the output.

Thank you for your consideration of my problem.